1. Field of the Invention
The invention relates to a process and a device for filling depressions, such as cups or grooves, on the cylindrical surface of a rotating, cylindrical body, such as a roller, cylinder or sleeve, with a fluid by means of a chamber located alone, the mantle of the cylindrical body and open towards the cylindrical body. Cylindrical bodies of this type can be, for example, the screen rollers of short inking units or gravure cylinders which are inked. However, use is also possible with damping or varnishing units, for example.
2. Description of the Prior Art
It is traditional in the case of gravure cylinders to use immersion inking with subsequent wiping off by means of a doctor blade (e.g., EP 0 114 329 B1). Apart from ink spraying or ink misting, this inking process is associated with ink blockage under the blade, especially during positive inking, i.e., when the doctor blade points in the rotational direction of the cylinder, because the cylinder delivers a considerably excessive quantity of ink and the new ink being constantly delivered prevents any backflow. The ink blockage causes the doctor blade to bend, and in order to compensate for this increased blade placement forces are required. These forces, in conjunction with the blocked ink, result in considerable abrasion of the type form. Furthermore, the hydrodynamic pressure of the ink blockage is dependent on the circumferential speed of the cylinder being inked, which leads to a speed-dependent knife pressure on the cylinder and thus to the known ink fluctuations as a function of speed in gravure printing. Finally, the cohesive forces of printing inks are in principle substantially greater than the adhesive forces to the typeform, for which reason, after a cup is filled, printing ink is essentially removed repeatedly from the cup surface, leading to at least a ten-percent underfilling of the cups.
Currently, the inking of anilox rollers is done with chamber blade systems in a great variety of designs on the basis of various principles. Thus, DE 92 16 754 U1 discloses a chamber blade in which both the working blade and the closing blade are placed on the screen roller negatively, i.e., opposite to the rotational direction of the screen roller, and the inking space is rectangular. In order to fill the chamber in a manner that is at least axially uniform, a higher chamber pressure burden must be ensured. However, this pressure in the chamber leads inevitably to the opening of the negatively placed closing blade and thus to an egress of ink, apart from the increased wear on the working blade. In addition, due to insufficient ink flow, ink clusters form in the chamber corners with air pockets that interfere with inking.
According to EP 0 324 140 B1, the attempt is made to achieve inking without pressure by installing a scoop roller in the chamber blade.
Other constructions, for their part, describe the necessity of built-in elements in the interior of the chamber blades. Thus, EP 0 315 091 B1 discloses an example with a blade chamber having an interior with a circular cross-section, in which there is a cylindrically shaped body which bears on and is driven by the anilox-roller. Other built-in elements of different shapes are also suggested. This design, too, is unable to ensure flawless functioning. Air necessarily makes its way into the interior space, on the one hand through the emptied cups, and on the other hand through the slip-stream on the cylinder surface. The ink that has flowed onto the screen roller in the interior space cannot freely exchange itself for air, but rather mixes with the air.
Furthermore, the ink accelerates in the gap to the built-in elements, so that relative movements take place between the ink and the cylinder surface which interfere with inking. Behind the gap created by the built-in elements, diffuse relaxation of the ink film occurs, with the result that the ink film, since it can flow off freely, has no reason to adhere to the surface up to the working blade. The ink will thus tend to flow off rather than to ensure uniform inking by collecting below the blade knife point.
DE 39 11 839 A1 discloses an inking device in which an ink application channel with an arc-shaped cross-section is located in a pressure-free washing box. This channel passes along the ink supplied via its length to a screen roller. Here, too, there are problems of air collection in the ink channel as well as problems of air influence on the path of the cups to a working blade optionally located at a distance from the ink application channel.